Specified National Childrens Study sample collection and other devices must be prescreened for selected metals and other specified environmental contaminants by lot. Once a lot is passed, that source of supplies may be stocked in the National Childrens Study warehouse and distributed to National Childrens Study Centers. Prescreening takes 50 random samples from each lot of each device and compares the results of each metal or other contaminant specified to the allowable contamination for the specific study (National Childrens Study). An estimated 15 different types of blood and urine collection, processing and storage devices will be tested (in some cases by 4 or 5 analytical methods). Each current device lot prescreening is the equivalent of testing 50 children for a variety of metals. For example, urine cryovials must be tested by four different analytical methods to cover all of the potential metals that may be tested in the future. Prescreening of one lot of one size cryovial represents the equivalent of testing 200 children for lead, cadmium and mercury. Continuing prescreening of replacement lots is anticipated as inventory is depleted or expires.